Rainwater harvesting: TTT

Subcatchment element as displayed in the TT menu

Storage element as displayed in the TTT menu

Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system can be integrated into a site plan as a storage element, using the TTT:

1. Create a subcatchment area to harvest rainwater. Maybe this is a one or more building rooftops?

• • Click on the subcatchment button and draw over the desired catchment area, close the are with a double click.

1. Specify the RWH cistern as the outlet for the subcatchment(s).

• • Clock on the Storage button and place it nearby to the associated catchment.

A RWH cistern as a storage element (key parameters)

Land Use
Roof (%)	100
Subcatchment
Outlet	Select the name of your RWH cistern storage element (see below)

A RWH cistern as a storage element

Stage Storage
Storage type	No removal
Catchment	In many scenarios this will be the roof area, delineated on the map as a 'subcatchment'.
?	Lined
Underlying soil	Any:This doesn't matter for RWH cistern systems
Evaporation factor	0
Suction head (mm)	0
Saturated conductivity (mm/hr)	0
Initial soil moisture deficit (fraction)	0
The dimensions of the rainwater cistern can be placed into the fields: Bottom elevation (m) Maximum depth (m) Initial water depth (m) The Curves table is designed to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m2) will remain the same throughout the depth.

Tank used to store rainwater (typically roof runoff) for later use.

Rainwater harvesting.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Abiotic transfer of water vapour to the atmosphere.